WEDNESDAY, Jan. 16 (HealthDay News) -- As the popularity of energy drinks has soared, so has the number of Americans seeking treatment in hospital emergency rooms after consuming these highly caffeinated beverages, federal health officials report.

Between 2007 and 2011, the number of ER visits more than doubled from roughly 10,000 to almost 21,000. In 2011, 58 percent of these ER visits involved energy drinks alone, while 42 percent also included drug or alcohol use.

Most of these cases involved teens or young adults, although there was an alarming spike in the number of people aged 40 and older showing up in the ER after consuming these drinks, according to the report from the U.S. Substance Abuse and Mental Health Services Administration. Symptoms ranged from insomnia, nervousness, headaches and fast heartbeats to seizures.

Energy drinks contain high amounts of caffeine that can stimulate both the central nervous system and cardiovascular system, experts note. Caffeine levels in energy drinks range from about 80 milligrams (mg) to more than 500 mg in a can or bottle, the report noted, while a 5-ounce cup of coffee contains 100 mg of caffeine and a 12-ounce soda contains 50 mg of caffeine, the report said.

The beverages can also have other ingredients that may boost the stimulant effects of caffeine, according to report.

Many doctors are concerned about the high levels of caffeine in energy drinks, which can cause a major increase in heart rate and drive up blood pressure, explained Dr. Suzanne Steinbaum, a preventive cardiologist at Lenox Hill Hospital in New York City.

"In anyone who has any underlying heart condition, these two effects can be deadly," she told HealthDay recently. "Know what you're drinking before you drink it."

Dr. Mary Claire O'Brien, a leading expert on energy drinks from Wake Forest Baptist Medical Center in Winston Salem, N.C., had this this to say about the findings.

"The issue is not the doubling of emergency department visits. That is the symptom," O'Brien said. "The 'disease' is the failure of the federal government to regulate energy drinks as beverages."

Adding to the problem is the fact that most consumers, especially the young adults who are targeted by the makers of these beverages, are not aware of the serious health risks involved, she noted.

Meanwhile, the American Beverage Association took issue with the report, which was released late last week.

"This report does not share information about the overall health of those who may have consumed energy drinks, or what symptoms brought them to the ER in the first place," the association said in a statement on its website. "In fact, it shows that 42 percent of the reported ER visits were by someone who had admitted to consuming alcohol or taking illegal substances or pharmaceuticals. However, there is no way to assess whether any of the remaining individuals chose not to report this fact, and the consumption of those substances along with energy drinks means the energy drinks may be irrelevant."

According to the report, pills were the most common drugs combined with energy drinks (27 percent), with 9 percent of those involving stimulants such as Adderall or Ritalin. About 10 percent of the visits included the use of illicit drugs, with 5 percent involving marijuana.

Males accounted for about two-thirds or more of energy drink-related ER visits during the four years. Visits for both males and females doubled between 2007 and 2011, from about 7,000 to nearly 15,000 visits for males and from nearly 3,000 to nearly 6,000 visits for females.

People aged 18 to 25 accounted for most of the energy drink-related ED visits, followed by people aged 26 to 39. However, the report found that visits by people aged 40 and older increased 279 percent over those four years, from nearly 1,400 to about 5,200.

Concerns about energy drinks have been heightened following reports last fall of 18 deaths possibly linked to the products, and two U.S. senators want the U.S. Food and Drug Administration to investigate the safety of these beverages, the Associated Press reported. The FDA said in a statement that it will review the safety of energy drinks this spring, the wire service reported.